Beginning ASP.NET 4.5 in CSharp and VB Opsylum

Exception Handling x 685
In the following exercise, you see how to use Try Catch Finally in your code.
TRY IT OUT
Handling Exceptions
In this Try It Out, you see how to write exception-handling code to catch problems with sending
e-mail. These problems may occur when the mail server is down, for example. To simulate a broken
mail server, you’ll temporarily use a nonexistent mail server name causing your code to crash.
You’ll try out the Try Catch Finally code in a separate page in the Demos folder so you can closely
watch its behavior. When you understand how it works, you’ll modify the ContactForm.ascx user
control and incorporate the exception-handling code there. The reason you write this code in the demo
page first is that the user control uses an Ajax UpdatePanel that shields users from the dirty details of
an exception by default, making it difficult to see what’s going on.
1. Create a new file in the Demos folder and call it ExceptionHandling.aspx. Base the page on your
custom template and set its Title to Exception Handling Demo.
2. Add a Label control to the main content area and set its ID to Message.
3. Switch to Design View and set up an event handler for the Load event of the page by double-clicking
the read-only area of the page. Then at the top of the file, add either an Imports or a using
statement for the System.Net.Mail namespace:
VB.NET
Imports System.Net.Mail
C#
using System.Net.Mail;
4. Add the following code to the event handler that VS created. Notice how this code is almost identical
to the code you added in the ContactForm.ascx user control, so you can save yourself some
typing by copying parts of the code from that file. Notice how the code passes "DoesNotExist" to
the SmtpClient’s constructor as an argument for the mail host. This is done deliberately to trigger
an exception.
VB.NET
Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
Dim myMessage As MailMessage = New MailMessage()
myMessage.Subject = "Exception Handling Test"
myMessage.Body = "Test message body"
myMessage.From = New MailAddress("you@example.com")
myMessage.To.Add(New MailAddress("you@example.com"))
Dim mySmtpClient As New SmtpClient("DoesNotExist")
mySmtpClient.Send(myMessage)
Message.Text = "Message sent"
End Sub
C#
protected void Page_Load(object sender, EventArgs e)